Antenna array aperture multiplexing transmission feed and receive systems



ug 4, 1970 K. G. scHRoEDER 3,522,610

ANTENNA ARRAY APERTURE MULTIPLEXING TRANSMISSION FEED AND RECEIVESYSTEMS Filed Aug. 23, 1967 2 Sheets-Sheet 1 R R E ya R S w m m N ww T Nn/f A 55E 55m G w, wm IQ: mm zo.. s VN ,.i, W ww UH M L K Aug 4, 1970 K.G. SCHROEDER 3,522,610

ANTENNA ARRAY APERTURE MULTIPLEXING TRANSMISSION FEED AND RECEIVESYSTEMS ATTORNEYS United States Patent O 3,522,610 ANTENNA ARRAYAPERTURE MULTIPLEX- ING TRANSMISSION FEED AND RECEIVE SYSTEMS Klaus G.Schroeder, Dallas, Tex., assiguor to Collins Radio Company, CedarRapids, Iowa, a corporation of Iowa Filed Aug. 23, 1967, Ser. No.662,764 Int. Cl. H01q 3/26, 2.7/00

U.S. Cl. 343-854 5 Claims ABSTRACT OF THE DISCLOSURE This inventionrelates in general to antenna variable aperture multiplexing, and inparticular, to antenna array aperture automatic, as a function offrequency, variable aperture multiplexing transmission feed and receivesystems.

With many wide band antenna array systems the effective aperturegenerally does not most effectively suit the particular frequency beingtransmitted or received. To do so requires that the effective aperturebe relatively narrow for the higher frequencies and be increased inwidth for the lower frequencies. Further, wide band antenna arraysystems using positive switching devices to vary the effective aperturegive a step function operational result in effective beam width, and,particularly with respect to relatively high power signal transmission,the requirement is imposed for relatively complex, heavy duty, andexpensive switching equipment in order to adequately perform therequired function.

It is, therefore, a .principal object of this invention to provide anautomatic variable aperture multiplexing antenna transmission feed andreceive system with the automatic aperture variation a function offrequency.

A further object of such an automatic antenna variable aperture systemis smooth operational transition from one frequency automaticallyactivated mode of operation to another frequency determined mode ofoperation.

Features of this invention useful in accomplishing the above objectsinclude, in various embodiments, automatic antenna variable apertureincrease with signal frequency change from a high frequency mode ofoperation to a low frequency mode of operation. This aperture increaseis to approximately twice the high frequency aperture with two addedelements at each end of the antenna array. Hybrid circuits interconnectthe added elements, and a low pass filter is included in the combinedcircuit path to a signal terminal, in the feed network, also connectedto the antenna array elements of the high frequency aperture middle.portion of the array. The spacing span of such an antenna array is,generally, twice the span of the high frequency element portion of thearray when the low frequency mode of operation is approximately one-halfthe high frequency mode of operation. Some embodiments also include highpass filtering in the combined circuit portion of the feed networkconnected to the antenna elements within the high frequency portion ofthe array.

Specific embodiments representing what are presently regarded as thebest modes of carrying out the invention are illustrated in theaccompanying drawings.

In the drawings:

f. ICC

FIG. 1 represents a schematic of an RF transmitting and/or receivingantenna array and the feed circuitry therefor with signal path meansfrom a single feed circuit terminal to a middle array element highfrequency aperture portion, and signal path circuitry between the singlefeed circuit terminal and outboard antenna array elements with low passfilter circuitry passing a low frequency mode range of operationalfrequencies through the signal path circuitry between the single feedcircuit terminal and the outboard antenna elements;

FIG. 2, a schematic of an antenna array very similar in many respects tothe antenna array and feed network embodiment of FIG. 1 with, however,high pass filter circuitry in the feed between the single feed networkterminal and the middle array element high frequency aperture portion ofthe antenna array;

FIG. 3, a schematic of an embodiment similar in many respects to theembodiment of FIG. 2 with, however, additional filter circuitryincluding a high pass filter section between the single feed point andthe middle array element high frequency aperture portion of the antennaarray, and in addition to a low pass filter circuit, such as employedwith the embodiment of FIG. 2, a further low pass filter circuitconnected between the circuit path extending between the single feednetwork terminal and the outboard antenna array elements and the circuitpath to the middle array element high frequency aperture portion at thejunction of the high pass filter section with that portion of theantenna array system; and,

FIG. 4, a plot of the signal energy distribution through respectivelythe high pass filter circuitry and the low pass filter circuitry such asemployed in the embodiment of FIG. 2 and such as passed by the high passfilter section and the low pass filter directly connected to the singlefeed circuit terminal in the embodiment of FIG. 3, with the pass bandsof the respective low pass and high pass filter sections overlapping andbeing complementary so that they cross in a middle frequency range witheach at substantially a -3 db level, and with each respective frequencyincreasing, or as the case may be, frequency decreasing signal energybeing passed, while overlapping for a range, continually decreasing withrespect to the frequency mode of operation the frequency shift is awayfrom while the other increases until at the outer limits of frequencyoperation the frequency is entirely passed by one filter section or theother filter section, respectively, as the case may be.

Referring to the drawing:

The RF transmitting and/or receiving antenna array 10 of FIG. 1 includesfour laterally spaced antenna groups 11 of antenna elements 12a and 12b,each, in a middle array element high frequency aperture portion 13 ofthe antenna array 10 and two groups 14 of two antenna elements 15a and15b, each, comprising outboard antenna array elements laterally spacedoutside the lateral spacing range of the middle array element highfrequency aperture portion 13. The antenna structure 10 also includes afeed circuit network connected between a single feed network terminal 16and the antenna array elements 12a, 12b, 15a and 15b. The single feedcircuit terminal 16 is connected to a hybrid circuit 17, of conventionalnature, that has a port connection to a further hybrid circuit 18. Inthe middle array element high frequency aperture portion feed networksection dual ports of the hybrid circuit 118 are in turn connected toadditional duplicate hybrid circuits 19a and 19b from which dual outputterminal ports in turn are connected to four further hybrid circuits20a, 20h, 20c and 20d, respectively, that have dual ports connected torespective antenna elements 12a and 12b of the respective antenna groups11. The other port of hybrid circuit 17 duplicating the port 18 isconnected to and through a low pass filter circuit 21 that may be afilter circuit such as a transmission line or a lumped constant circuitconfiguration in accord with conventionally known filtering techniques,detail not shown, to hybrid circuit 22 equipped with dual portsconnected respectively to hybrid circuits 23a and 23b of the outboardantenna eletrnent groups 14 at the opposite outboard sides of theantenna array 10. With the antenna array configuration and the feed orcombining network associated therewith the middle array element highfrequency aperture portion 13 is used throughout the entire operationalfrequency range of the antenna array both in the high frequency areamode of operation and also in the low frequency mode of operation andfor the intermediate transitory area of operation, while, the outboardantenna array elements 15a and 15b come into effective usage only in thelow frequency area mode of operation with signal energy beingeffectively passed through low pass filter 21.

'Referring now to the embodiment of FIG. 2 wherein the antenna array 10is very similar to the antenna array 10 of FIG. l with the only reallysignificant changes being that the hybrid circuit 17 is removed and ahigh pass filter 24 is employed, with the single feed network terminal16 connected directly in common to both the low pass filter 21 and thehigh pass filter 24 and with the other side of the high pass filter 24connected to the hybrid circuit 18. With this embodiment portions of theantenna array and the feed or combining circuitry are numbered the sameas a matter of convenience and much of the explanation as applied to theembodiment of FIG. 1 is applicable in the same fashion with respect tothe embodiment of FIG. 2. Please note at this point, however, that withthe embodiment of FIG. 2 the middle array element high frequencyaperture portion 13 is not used throughout the entire operationalfrequency range of the antenna array, and is used only through the highpass signal energy effective passing range of the high pass filtercircuit 24. The two filters, the low pass filter 21 and the high passfilter 24, as connected and used in this circuit provide a simple highpass-low pass type complementary filter circuit structure useful incombining the signal from a basic eight port corporate feed connected tothe high band center portion of the laterally extended bandwidth array,and with the signal from a four port corporate feed connected to the lowband extension of the antenna system.

(Referring further to still another embodiment, that of FIG. 3, thereare again many similarities between this antenna and the embodiments ofboth FIGS. 1 and 2. With this being the case, just as with the em-lbodiment of FIG. 2 components of FIG. 3 the same as with the embodimentsof FIGS. l and 2 are numbered the same as a matter of convenience, andthose numbers performing a similar function are in some instances givena primed number. With this embodiment, the single feed network terminal16 is connected directly in common to both the low pass -lter 21 and thehigh pass filter section 24'. The filter section 24' may include twohigh pass filter circuits 25 and 26 interconnected by a length of signaltransmission line 2.7 in order to optimumly minimize the stub length ofleads from the respective high pass filter circuits 25 and 26. Theconnective leads involved include their connections, respectively, withthe terminal 16 and the common junction of hybrid circuit 18 and anadditional low pass filter 28. The low pass filter 28 is connectedbetween the common junction of high pass filter circuit 26, of the highpass filter section 24', with hybrid circuit 18 and a port of hybridcircuit 29 another port of which is connected to hybrid circuit 22.Hybrid circuit 29 also has a terminal connection with and through lowpass filter 21 to the common junction of the single feed networkterminal 16 and the high pass filter 25 of high pass filter section 24'.

It is interesting to note at this point the plot of signal energydistribution of FIG. 4 with respect to high pass filter circuitry andlow pass filter circuitry that are selected to be advantageouslycomplementary when ernployed as the low pass filter circuit 21 and thehigh pass filter circuit 24 of the embodiment of FIG. 2 and as the lowpass filter circuit 21 and the high pass filter circuit section 24 ofthe embodiment of FIG. 3. This is with the pass bands of the respectivelow pass and high pass filter sections overlapping and beingcomplementary so that they cross in a middle frequency range with eachat substantially a -3 db level. Further, as the operational frequency isshifted in the direction of one frequency mode, the overlappingfrequency of the opposite mode of operation decreases in energy contentuntil substantially the entire energy content is being passed solely bythe filter for the mode of operation towards which the frequency shifthad been occurring. Obviously desired design and operating criteria forsome antenna array installations and usage may call for, in someinstances, some departure from the complementary relation between thehigh pass and low pass filters described here without materiallydeparting from the inventive concepts presented by applicants teachingsherein. Please note further that low pass filter 2.8 in the embodimentof FIG. 3 in most instances is advantageously designed to passsubstantially the same frequency range passed by the low pass filtercircuit 21 in order to provide equal division of signal energy betweenthe ports of the hybrid circuit 29 connected to hybrid circuit 22 andthrough the low pass filter 28 to the hybrid circuit 18, respectively.

The three embodiments of FIGS. 1, 2 and 3 are three array and feedcombiner network systems having many features in common for extendingthe low frequency aperture of an antenna array and thereby narrowing thebeamwidth at the low end of the operational frequency band. With theparticular antenna element spacings employed for eight elements in thecenter sections, shown as a. middle array element high frequencyaperture portion 13, the element spacing was such as to provide certaindesired antenna array results in accord with antenna spacing criteriaknown to those skilled in the art. Further, in the embodiments shown thespacing of two additional elements laterally spaced to each side of thecenter section are shown as having twice the spacing for an apertureincrease to twice the high frequency aperture with this structuralapproach. Obviously this can be varied one direction or the other asdesired by variances in the spacings for particular criteria or in orderthat operational design requirements are anticipated. With theparticular antenna element spacings employed in the embodiments of FIGS.1, 2 and 3 and with, in the embodiments of FIGS. 2 and 3, the llow passand high pass filter circuits being compatible as has been discussed,there is at least one point or area of operation where Substantiallyonly half the power applied to each of the four outer elements isapplied to each of the center elements, and that when all elements areexcited the power density is substantially constant across the arraysince the element spacing in the center is half the spacing of the outerlower frequency mode of Operation elements. Obviously as has beensuggested and described at least to some extent hereinbefore there maybe variations in power feed division of signal power energy feed withrespect to the different elements with variations in the spacing withoutmaterially departing from applicants teachings herein presented.

At least in a sense with the type of performance attained, structuralarrangement and feed, some of the antenna structures may be consideredas being akin to a log periodic broadside array in a directionperpendicular to the wave front. If a number of antenna elementextensions are used each with the same element-to-element spacing andelement-to-reector spacing in terms of wavelengths at the centerfrequency of each sub band, the analogy is particularly pertinent. Withthese antenna array configurations and feed systems, the dimensions ofthe structure in the direction of propagation are minimized.

However, in comparison to various other approaches that have lbeenemployed, there is substantially no limit for the azimuth beamwidthbecause all elements are radiating in the same direction and, it is ofinterest to note that, with the addition of variable phase controllingcircuitry of a conventional nature (not shown) with the variousernbodiments, the beam can be slewed. With these embodiments instead ofslow wave active cell separation as in an endfire log periodic antenna,the separation of active.

regions is accomplished in the feed network by transmission line orlumped constant filtering techniques, as has been set forthhereinbefore. By way of reiteration to some extent substantiallycomplete freedom of design is available with respect to choice ofcrossover frequencies in the interacting area of the active region withthe embodiments of FIGS. 2 and 3 so that, for example, a limited numberof narrow operating frequency bands (as in International Broadcasting)minimum azimuth beamwidth variation can be accomplished at some moderateincrease in equipment cost. An additional interesting fact is that withthese antenna array structures the real estate requirements aresubstantially the same as those imposed for a low frequency arrayantenna cell system alone.

With the FIG. 2 embodiment an eicient high pass-low pass typecomplementary filter feed network circuit is used to combine the signalfrom a basic eight point corporate feed connected to the high bandcenter portion of the extended bandwidth array with the signal from afour port corporate feed connected to the low band extension. With thisapproach it should be noted that the crossover band must be fairly broadand the elements must be fairly close together, or grating lobes willoccur at the low end of the extended operating band. Further, this in auincreasing problem with an increasing number of elements in the highband array. The embodiment of FIG. 1 is one solution to this limitationwith both array sections obviously being used at the low end of theoperational frequency band. With this approach a loss in absolute gainof approximately 3 db is suffered at the high frequencies, but if cutofffrequency is chosen properly the gain should still be higher than theminimum absolute gain at the low end of the band.

With reference again at this point to the embodiment of FIG. 3, this isan embodiment utilizing full automatic crossover with both subarraysutilized at the low frequencies and with loss being kept quite minimalsince the complementary filters are actually low loss devices. Thecomplementary ring lter circuit configuration with the filter section 24including filter circuits 25 and 26 and the low pass filter 21 alongwith the low pass filter 28 in the embodiment of FIG. 3 constitutes,generally speaking, an optimum receiving diplexer circuit with respectto the operational frequencies of the antenna array This is particularlyso with the two high'pass filters 25 and 26 in the filter section 24'being so design selected as to work into each other instead of standardmatched loads.

Whereas this invention is here illustrated and described with respect tospecific embodiments thereof, it should ybe realized that variouschanges may be made without departing from the essential contributionsto the art made by the teachings hereof.

I claim:

1. In a variable aperture transmission-receive antenna array system withautomatic, as a function of frequency, aperture variation from a narrowhigh frequency mode of operation to a relatively wide low frequency modeof operation, a middle array element high frequency aperture portlonconnected to a feed network terminal; outboard antenna array elementsspaced outside the lateral spacing range of said middle array elementhigh frequency aperture portion; hybrid circuit means interconnectingsaid outboard antenna array elements; low pass filter means connected inthe feed circuit between said feed network terminal and said outboardantenna array elements; wherein an additional hybrid circuit is providedin the feed network between said low pass filter means and said feednetwork terminal; and with said additional hybrid circuit having a portconnection to the middlehigh frequency aperture portion of the antennaarray system.

2. In a variable aperture transmission-receive antenna array system withautomatic, as a function of frequency, aperture variation from a narrowhigh frequency mode of operation to a relatively wide low frequency modeof operation, a middle array element high frequency aperture portionconnected to a feed network terminal; outboard antenna array elementsspaced outside the lateral spacing range of said middle array elementhigh frequency aperture portion; hybrid circuit means interconnectingsaid outboard antenna array elements; low pass filter means connected inthe feed circuit between said feed network terminal and said outboardantenna array elements; wherein circuit means provides a signal path forlow frequency signal energy ybetween said feed network terminal and saidmiddle array element high frequency aperture portion of the array systemwhen the system is in the low frequency mode of operation.

3. The variable aperture antenna array system of claim 2, wherein highpass filter means is connected in the feed circuit between said feednetwork terminal and the middle array element high frequency apertureportion of the antenna array system; and a low pass filter connected inthe feed circuit between said feed network terminal and the middle arrayelement high frequency aperture portion of the antenna array system.

4. The variable aperture antenna array system of claim 3, wherein saidlow pass filter means is connected between said feed network terminaland a hybrid circuit having a port connected to said low pass filterconnected in the feed circuit between said feed network terminal and themiddle array element high frequency aperture portion of the antennaarray system.

5. The variable aperture antenna array system of claim 3, wherein saidhigh pass filter means includes two high pass filters interconnected bya length of signal transmission line.

References Cited UNITED STATES PATENTS 2,096,031 10/1937 Cork 343-8533,255,450 6/1966 Butler 343-853 X FOREIGN PATENTS 1,031,031 6/ 1958Germany.

1,074,676 2/ 1960 Germany.

ELI LIBERMAN, Primary Examiner T. I. VEZEAU, Assistant Examiner U.S. C1.X.R. 343-844

